I have an 83 cj7 it came stock with a 258 inline six cylinder , t4 tranny and a dana 300 xfer case.i put a 304v8 in her.I also put moser one piece axles in the model 20 rear.Can anyone tell me what gear ratio i have in my model 20 rear? could it be 3:73?

I've read that you have to look at the tag on the axle. Sometimes they say it's stamped on a flat spot to the right of the pumpkin as it appears from the rear end of the Jeep. Please correct me if I'm wrong - If you can't find a tag or scrape away enough mud/rust etc., you can try jacking up one rear wheel and turning it while counting the turns of the wheel until you see one full turn of the input shaft on the rear end.

If it takes almost 4 full turns to make one on the input shaft, you probably have 3:73's. It it takes a little more than 4 turns, it's probably a 4:10. Remember to put your transfer case in N so the drive shaft will turn without a bind. If you have a locker, you will have to jack up both wheels and turn one (correct me if I'm wrong).

Also, you can jack up one rear wheel, and do that thingy where you rotate the tire once, and se how many time the driveshaft turns. If its less than 3, its likely 2.73, if its a little over 3, it 3.31, 3 1/2 times, 3.54, and so on . . .

THANKS ILL TRY THAT.I WENT TO THAT MODEL 20 WEB PAGE IT SAYS THAT THE MODEL 20 COULD BREAK AT THE TUBES .TO FIX THE PROBLEM U HAVE TO WELD THE TUBES TO THE POT,MY NEXT QUESTION IS CAN I WELD THEM WITHOUT TAKING MY REAR APART?

william if you know that it is stock, except for the one piece's it will have ethier a 3.54 or 3.73.
the sure way to know is remove the diff cover. and count the ring gear teeth.
if there is 39 teeth on the ring gear it has a 3.54 ratio.
if there is 41 teeth it has a 3.73 ratio.
(the pinion will have 11 teeth for both)

To answer that question - probably not. I've never heard of anyone welding a axel while it is still together. Usually people take them to an axel shop that specializes in that stuff and they have them re-work it the way you want it. Most do-it-yourselfers don't have the expertise to weld and machine axels like a shop. Many do-it-yourselfers do replace parts in their axels and perform bolt on upgrades, but most don't tackle machining and welding modifications to their axels.

2cjs, I have an 85 CJ7 w/ 258, dana300, T5, AMC 20, and AC. It is stock and has no tags or visible markings on the axle. I have tried jacking up the drivers side rear tire, marking it & the driveshaft, and spinning them. I did this several times and always got the same results. The trouble was that the results were that I have about a 1.3:1 ratio. I know this can't be right but that is what I got. Maybe jacking up the whole rearend will give a different number. I haven't had time to check it out but maybe it will help you.

Originally posted by 2cjs:THANKS ILL TRY THAT.I WENT TO THAT MODEL 20 WEB PAGE IT SAYS THAT THE MODEL 20 COULD BREAK AT THE TUBES .TO FIX THE PROBLEM U HAVE TO WELD THE TUBES TO THE POT,MY NEXT QUESTION IS CAN I WELD THEM WITHOUT TAKING MY REAR APART?

Yes you can - I weld cast iron to steel all the time. You have to preheat the casting to close to 600 degrees before attemping to MIG weld it. Flux core wire is a bonus here due to the inherent "dirtyness" of cast iron. MIG with an CO2 & argon mix will work though.